LDL plays a main role in transportation of cholesterol in blood and most of the cholesterol deposited on the blood vessel wall in pultaceous arterial sclerosis is originated from LDL. Increase in the amount of LDL in plasma is one of the major risk factors in pultaceous sclerosis such as ischemic heart disease, so that separate quantification of LDL cholesterol is clinically important.
Conventional methods for quantifying LDL cholesterol include a method comprising two steps, that is, a fractionation operation and an operation for quantifying the cholesterol, and a method in which the blood levels of total cholesterol, HDL cholesterol and triglyceride are determined and the amount of the LDL cholesterol is determined according to the Friedewald's equation.
Fractionation operation includes ultracentrifugation method, precipitation method, immunochemical method and the like. In the ultracentrifugation method, LDL is separated exploiting the difference in the specific gravity by an ultracentrifuge, and the amount of the cholesterol therein is measured. In the precipitation method, anti-HDL antibody, polyanion and a divalent cation are added to form an insoluble precipitate, and the LDL cholesterol in the supernatant after centrifugation is quantified (WPI Acc No.85-116848/20). In the immunochemical method, anti-HDL antibody, anti-VLDL antibody and anti-CM antibody are bound to latex particles, and the latex particles are removed by centrifugation or by passing through a filter after agglutination, followed by quantifying the LDL cholesterol (WPI Acc No. 84-301275/49). However, these conventional methods are problematic in simplicity or cost.
According to the Friedewald's equation, the amount of LDL cholesterol is calculated by subtracting the amount of the HDL cholesterol from the amount of the total cholesterol, and then further subtracting the 1/5 of the amount of the triglyceride. However, since this method does not take the influence by the diet and the individual difference, this method is problematic in accuracy.
Recently, a method for quantification of LDL cholesterol, which does not require fractionation operation, has been reported (WPI Acc No. 83-766269/38). However, in this method, the specificity to LDL is not sufficient.